1 ABSTRACT The world's population will increase to 9.4 billion people by 2050 and 70% of whom will be living in urban areas. Such urbanization with population growth and industrial development demands in turn create a need for the planning, design, and construction of environmental infrastuctures (e.g., water and wastewater treatment plants: WTPs and WWTPs). The environmental infrastructures are essential to provide cities and towns with water supply, waste disposal, and pollution control

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... es. During the operation of WTPs and WWTPs, massive amount of energy, fuels, and chemicals are consumed. Therefore, they could be major contributors to urban greenhouse gas (GHG) emissions (i.e., 17% of GHGs are generated from water and sewer sector in urban area). To make cities resilient and sustainable, the emission of GHGs from WTPs and WWTPs should be estimated as accurately as possible and effective mangement plans should be set up as soon as possible. A comprehensive model was developed to quantitatively estimate on-site and off-site GHGs generated from WTPs and WWTPs. The model was applied to an advanced WTP (treating 200,000 m³/d of raw water with micro-filtration membrane) and a hybrid WWTP (treating 5,500 m³/d of municipal wastewater with five-stage Bardenpho processes). The overall on-site and off-site GHG emissions from the advanced WTP and hybrid WWTP were 0.193 and 2.337 kgCO 2 e/d*m3. The major source of GHG generation in the advanced WTP was off-site GHG emissions (98.6%: production of chemicals consumed for on-site use and electricity consumed for unit-process operation). On the other hand, on-site GHG emissions related to biochemical reactions (64%) was the main GHG source of the hybrid WWTP. Reducing electricity consumption in advanced WTPs could be the best option for generating less GHG emissions and acquiring better water quality. Various options (CO 2 capture and conversion to other useful materials, recovery and reused of CH 4 , and operation of WWTPs at optimal conditions) could significanlty reduce the total amount of GHG emissions in hybrid WWTPs. The results could be applied to the development of green and sustainable technology, leading to a change in paradigm of urban environmental infrastructure. Keywords: wastewater treatment plant, water treatment plant, urban environmental infrastructure, greenhouse gas, sustainable technology 2 METHODOLOGY 2.1 System boundary The system boundaries and the emission pathways of the advanced WTP and hybrid WWTP are demonstrated in Fig. 1 and 2. The system boundary of advanced WTP includes a chemical supply, a rapid mixing, a flocculation, a micro-filtration (MF) membrane, and an ozone disinfection process. In case of the hybrid WWTP, this includes a primary clarifier (PC), a five-stage Bardenpho process [anaerobic (ANAE), first anoxic (ANOX1), first aerobic (AER1), second anoxic (ANOX2), and second aerobic (AER2) stages], a second clarifier (SC), a filter bed (FB), and a ultraviolet disinfection (UVD) process. The baseline task of WTP was treating 200,000 m3/d of raw water with 10 NTU to 0.005 NTU and that of WWTP was dealing with 5,500 m³/d of wastewater (200 mg/L influent BOD) to meet the effluent standard (less than 10 mg/L BOD, 20 mg/L TN, and 0.5 mg/L TP). Typical operating conditions and parameters of the WTP and WWTP in South Korea were used to estimate GHG emissions. 2.2 Estimation of GHG emissions from the WTP and WWTP There are two types of GHG emissions generated from the WTP and WWTP. We define on-site GHG emissions stem from biochemical reactions in unit processes. Off-site GHG emissions are due to consumption of electricity and fuel for unit process operations as well as for the production and transportation of chemicals for on-site consumption. We developed a comprehensive model for the accurate